Cellular differentiation and normal development are functions of variable gene activity, and this proposal addresses questions relating to the processes which sustain regulated variable gene expression in eukaryotes. Specific emphasis is placed upon translation-level events. The long range goal of this project is to attempt to determine the molecular basis of differential gene activity in eukaryotes by characterizing the mechanisms which permit selective, high efficiency regulation of gene activity. Variable gene activity is evident during normal development as specific subsets of genes are activated and a progression of increasing complexity of form is observed. Moreover, defects in developmental processes, or abnormal forms of tissue development such as malignant tumors, have a basis in molecular aspects of gene expression. Ideally, the long range goals of this project are consistent with improving capabilities for diagnosis, treatment, or prevention of human disease, or with the development of new technology for production of biological materials for use in medicine, industry, or agriculture. The immediate goal of this work is to characterize those features of messenger RNA (mRNA) sequence and/or structure which are located in or near the 5' non-translated leader and which play a major role in determining the initiation efficiency and therefore, the translational efficiency, of a given mRNA. The features of mRNA which will be considered include both primary nucleotide sequence, involving modifications such as 5' "capping" by m GpppN, and secondary structure (base pairing) of deproteinized mRNA. Moreover, specific mRNA-cap binding protein complexes will be analyzed to determine both the topography of specific protein binding sites and to directly detect the presence or absence of structural changes elicited by protein binding. These approaches are aimed at determining why some mRNAs are translated with greater efficiency than others and, in addition, to ascertain whether it seems feasible to exploit these findings for increased selective expression of biologically important proteins.